Abstract
Although cells isolated from fetal liver are one of the major sources for liver tissue engineering, it is still very difficult to induce them to fully differentiate in vitro into mature hepatocytes. We therefore investigated the effects of nicotinamide (NA), dimethyl sulfoxide (DMSO), and oncostatin M (OSM) on differentiation in terms of the expression of various liver-specific functions, because these factors have been reported to induce the emergence of possible hepatocyte progenitor cells (small hepatocytes) in adult rat hepatocyte culture or maturation of fetal mouse liver cells in culture. Fetal liver cells isolated from mouse embryos were cultured for 5 weeks in collagen-precoated plates. NA (10 mM) and DMSO (1%) remarkably enhanced the emergence of small hepatocytes, and OSM also synergistically enhanced the selective growth of small hepatocytes and inhibited the growth of blood cell populations. In the presence of these three factors, such small hepatocytes became dominant in culture, so that they covered almost 60–70% of confluence after week 2. In addition, some of them piled up over the small hepatocyte monolayer and displayed distinctively differentiated morphology, such as the emergence of binucleated cells, formation of tight gap junctions, and possible bile duct structures. Although OSM alone had very weak effects on hepatocyte functions, albumin secretion and cytochrome P450IA1/2 capacity were greatly enhanced when combined with NA or DMSO. This functional observation closely agreed with the emergence of small hepatocytes. In contrast, ammonium removal was strongly dependent on DMSO alone. DNA amount basis functions of fetal cells with three factors at week 5 were 1/7 for albumin secretion, 3 times higher for ammonium removal, and 1/10 for P450 capacity, compared with those of cultured adult mouse hepatocytes. These results show that inclusion of NA, DMSO, and OSM in the culture medium significantly enhances in vitro maturation of fetal liver cells when compared with conventional culture conditions.